Components of many electronic, electro-mechanical, and optical devices and systems need to be assembled with precise alignment to assure optimal performance. In the case of certain magnetic recording disk drives, for example, a read/write head needs to be carefully positioned with respect to a surface of a disk during use to assure optimum performance and to avoid crashing the head into the disk and causing damage.
Magnetic disk drives that utilize a head assembly for reading and/or writing data on a rotatable magnetic disk are well known in the art. In such drives, the head assembly is typically attached to an actuator arm by a head suspension assembly. A head suspension assembly includes a head suspension and an aerodynamically designed slider onto which a read/write head is provided so that the head assembly can be positioned very close to the disk surface. Such a head position during usage, that is, where the head is positioned over a spinning disk, is defined by balancing a lift force caused by an air bearing that spins with the disk acting upon the aerodynamically designed slider and an opposite bias force of the head suspension. As such, the slider and head fly over the spinning disk at precisely determined heights.
Head suspensions generally include an elongated load beam with a gimbal flexure located at a distal end of the load beam and a base plate or other mounting means at a proximal end of the load beam. According to a typical head suspension construction, the gimbal flexure comprises a platform or tongue suspended by spring or gimbal arms. The slider is mounted to the tongue thereby forming a head suspension assembly. The slider includes a read/write magnetic transducer provided on the slider and the slider is aerodynamically shaped to use an air bearing generated by a spinning disk to produce a lift force. During operation of such a disk drive, the gimbal arms permit the slider to pitch and roll about a load dimple or load point of the load beam, thereby allowing the slider to follow the disk surface even as such may fluctuate.
The head slider is precisely mounted to the flexure or slider mounting tongue of a head suspension at a specific orientation so as to fly at a predetermined relationship to the plane of the disk surface. During manufacturing and assembling of the head suspension assembly, any lack of precision in forming or assembling the individual components can contribute to a deviation in the desired relationship of the surfaces of these components. A buildup of such deviations from tolerance limits and other parameters in the individual components can cause a buildup of deviation from the desired relationship of the head slider to the associated disk surface in the complete head suspension assembly. The parameters of static roll attitude and static pitch attitude in the head suspension assembly generally result from these inherent manufacturing and assembly tolerance buildups.
Ideally, for optimum operation of a disk drive as a whole, during assembly of a head slider to a slider mounting tongue, the plane of a load beam mounting surface datum and the plane of a head slider surface datum should be in a predetermined relationship to each other. The load beam mounting surface datum and the slider surface datum are usually planar surfaces that are used as reference points or surfaces in establishing the relationship of the plane of an actuator mounting surface and the plane of the surface of the head slider surface relative to each other. The upper and lower planar surfaces of the head slider are also manufactured according to specifications usually requiring them to be essentially or nominally parallel to each other.
In practice, several optical methods can be used to measure the angle of component surfaces, such as laser triangulation or interferometry. Another optical method that can be used is known as autocollimation. An autocollimator is able to measure small surface angles with very high sensitivity. Light is passed through a lens where it is collimated prior to exiting the instrument. The collimated light is then directed toward a surface, the angle of which is to be determined. After being reflected by the surface to be measured, light enters the autocollimator and is focused by the lens. Angular deviation of the surface from normal to the collimated light will cause the returned light to be laterally displaced with respect to a measurement device such as a position sensing device. This lateral displacement is generally proportional to the angle of the surface and the focal length of the lens. An advantage of such a device is that the angle measurement is independent of the working distance of the lens or the distance between the instrument and the component being measured. However, one limitation of this type of device is that it is difficult to use and to measure poorly reflective or non-reflective surfaces.
In the case of measuring the angle of a surface for receiving a slider, accurate information for the mounting or attachment area of the surface is desired. In typical autocollimator based static attitude measurement, the angular information for the mounting area is provided as an average angle for the mounting area. In certain cases, however, it may be desirable to measure the angle of more specific or distinct location of the mounting area such as if the mounting area has small or localized high points on the surface. Such localized high points could affect the angle of a slider mounted to the surface.